7. Define Primary Key? The primary key is the columns used to uniquely identify each row of a table. A table can have only one primary key. No primary key value can appear in more than one row in the table. 8. Define Unique Key? Unique key is a one or more column that must be unique for each row of the table. It is similar to primary key. Primary key column will not accept a null. Whereas the unique key column will accept a null values. 9. Define Foreign Key? A foreign Key is a combination of columns with value is based on the primary key values from another table. A foreign key constraint also known as Referential Integrity Constraint. 10. Define View? A View is a database object that is a logical representation of a table. It is derived from a table but has no longer of its own and often may be used in the same manner as a table. A view is a virtual table that has columns similar to a table. A view does not represent any physical data. 11. Compare and contrast TRUNCATE and DELETE for a table? Both the truncate and delete command have the desired outcome of getting rid of all the rows in a table. The difference between the two is that the truncate command is a DDL operation and just moves the high water mark and produces a now rollback. The delete command, on the other hand, is a DML operation, which will produce a rollback and thus take longer to complete. 12. What is cursors? Cursor is a database object used by applications to manipulate data in a set on a row-by-row basis, instead of the typical SQL commands that operate on all the rows in the set at one time.
Posted on: Tue, 13 Aug 2013 17:00:03 +0000
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